Towards a Precision Measurement of the Lamb Shift in Hydrogen-Like Nitrogen

Abstract

Measurements of the 2S _1/2-2P _1/2 and 2S _1/2-2P _3/2 transitions in moderate Z hydrogen-like ions can test Quantum-Electrodynamic calculations relevant to the interpretation of high-precision spectroscopy of atomic hydrogen. There is now particular interest in testing calculations of the two-loop self-energy. Experimental conditions are favorable for a measurement of the 2S _1/2 - 2P _3/2 transition in N ⁶⁺ using a carbon dioxide laser. As a preliminary experiment, we have observed the 2S _1/2 - 2P _3/2 transition in ¹⁴ N ⁶⁺ using a 2.5 MeV/amu foil-stripped ion beam and a continuous-wave CO₂ laser operating on the hot band of ¹²C¹⁶O₂. The measured value of the transition centroid, 834.94(7) cm^-1, agrees with, but is less precise than theory. However, the counting rate and signal-to-background ratio obtained indicate, that with careful control of systematics, a precision test of the theory is practical. Work towards constructing such a set-up is in progress.